Piezoelectric crystal element



y 1943- s. c. HIGHT 2,320,080

PIEZOELECTRIC CRYSTAL ELEMENT Original Filed Sept. 18, 1940 FIG. 2

2 (BO/LING ACID) lNl ENTOR 5 (6. HIGH 7' 8V ATTORNEY atented May 25, 3943 more : 1 rhea ll Telephone Laboratories,

incorporated,

New York, N. Y., a corporation at New YQBlilii @riginal application September l8, loco, Serial No. 351,251. gust ll,

13 (Clair-iris 'Hlis invention relates to piezoelectric crystal elements, such as for example, quartz or tourmaline piezoelectric crystal elements, and particularly to boiling such crystal elements to reduce frequency changes therein.

This application is a division of my copending application for Piezoelectric crystal apparatus, Serial No. 357,251, filed September 18, 1940.

(Due of the objects of this invention is to reduce the temporal frequency drift in piezoelectric crystal elements and to increase the frequency stability thereof.

Another object or this invention is to reduce strains in piezoelectric crystal elements.

Another object of this invention is to cleanse the surfaces of piezoelectric crystal elements.

in accordance with this invention, quartz or other piezoelectric crystal elements may be boiled in acid, such as in strong sulphuric or chromic acid, or in other solutions having a relatively high boiling point, in order to prevent or reduce changes in the frequency thereof due to aging effects, and to relieve or reduce strains in the crystal material.

For a clearer understanding of the nature of this invention and the additional advantages, features and objects thereof, reference is made to the following description taken in connection with the accompanying drawing, in which like reference characters represent like or similar parts and in which:

Fig. l is a perspective view of a bare piezoelectrio crystal element 9 which has beencut and ground to the correct dimensions to give the desired vibrational frequency; and

Fig. 2 is a view shovl ing the crystal element l oi Fig. l immersed in a bath 2 of boiling acid contained in a suitable container or beaker 3.

Newly cut crystal elements such as the crystal element l of Figs. 1 and 2 gradually change their frequency slightly and drift in frequency over a period of time of several days, but may be artiflcially aged by boiling the bare quartz crystal element l in a solution of acid 2, such as strong sulphuric acid or chromic acid in order to reduce the period of time that would otherwise be required for the crystal element l to acquire frequency stability, and to prevent a possible frequency drift outside of the allowable frequency limits after installation. cillation of untreated quartz crystal elements ordinarily slightly increases for about a week or so before the crystal reaches frequency stability in operation, but the frequency thereof may be increased about the same magnitude by initially The frequency of os- Divided and this application Alli ill-ll, Serial No. 4%,298

boiling it, in the uncoated state, for a short time in strong chromic or sulphuric acid, thus in effect artificially aging the crystal in a short time. Starting with the unplated crystal 1] immersed in the cold acid bath '2, the acid bath 2 may be gradually brought to a boiling condition and then allowed to cool before removing the crystal plate therefrom. Since the acid bath 2 boils at a temperature of the order of about 300 centigrade, the crystal plate l is put through a thermal cycle which tends to relieve or reduce strains in the quartz. Also, the boiling liquid 2 having zero surface tension probably works under and breaks loose minute fragments on the quartz surfaces. Whatever may be the explanation of the action of boiling the quartz plate l in acid, there is very little drift or change in frequency during the operation of the quartz plate t after being subjected to such treatment. For example, the operating frequency change in an unboiled l0 megacycle per second thickness-mode AT-cut crystal l over a period of ten days has been found to be of the order of 300 to 209 cycles per second, whereas the operating frequency change for such a crystal element after being boiled in strong sulphuric or chromic acid, for example, has been reduced to about 10 per cent of the values mentioned, or about 30 cycles per second over the same operating period. The reduction in frequency change occurs mostly during the first boiling in the acid and if boiled again in the acid bath, little further eiiect is obtained.

fidthough this invention has been described and illustrated in relation to specific arrangements, it is to be understood that it is capable of application in other organizations and is therefore not to be limited to the particular embodimerits disclosed, but only by the scope of the appended claims and the state of the prior art.

What is claimed is:

1. The method of cleaning a piezoelectric crystal element which comprises boiling it in a liquid bath at a temperature in excess of 100 centigrade.

2. The method of cleaning a piezoelectric crystal element which comprises boiling it in a liquid bath of acid at a temperature in excess of 100 centigrade.

3. The method of cleaning a piezoelectric crystal element which comprises boiling it in a liquid bath .of sulphuric acid at a temperature in excess of 100 centigrade.

4. The method of cleaning a piezoelectric crystal element which comprises boiling it in a liquid bath of chromic acid at a temperature in excess of 100 centigrade.

5. The method of treating a piezoelectric crystal element which comprises exposing it to the action of boiling acid at a temperature in excess of 100 centigrade, whereby frequency changes therein are eliminated or diminished.

6. The method of treating a piezoelectric crystal element which comprises exposing it to the action of boiling acid at a temperature of the order of 300 centigrade, whereby frequency changes and strains in the crystal element are eliminated or diminished.

7. The method of treating a. piezoelectric crys tal element which comprises exposing it to the action of boiling acid including one of the acids sulphuric and chromic at a temperature of the order of 300 centigrade, whereby frequency changes and strains in the crystal element are eliminated or diminished. 4

8. The method of treating a piezoelectric crys-- tal element which comprises immersing it in a bath of liquid, and bringing the liquid bath to a boiling condition at a temperature in excess of 100 centigrade, whereby the surfaces of the crystal element are cleansed.

9. The method of treating a piezoelectric crystal element which comprises immersing it in a bath of strong acid, and bringing the acid bath to a boiling condition at a temperature in excess of 100 in the crystal element are diminished.

0. The method of treating a piezoelectric crystal element which comprises immersing the crystal element in anacid bath having a boiling point temperature in excess of 100 centigrade, bringing the acid bath to a boiling condition at said temperature, and allowing the acid bath to cool before removing the crystal element therefrom, whereby frequency changes and strains in the crystal element are reduced.

1 The method in accordance with claim 10, wherein said bath is strong sulphuric acid.

12. The method in accordance with claim 10, wherein said bath is strong chromic acid.

13. The method of treating a piezoelectric crystal element which comprises immersing the crystal element in a liquid bath having a boiling point temperature of the order of 300 centigrade, bringing the liquid bath to a boiling condition at said temperature, and allowing the liquid bath to cool before removing the crystal element therefrom, whereby frequency changes and strains in the crystal element are reduced.

STUART C. HIGHT.

centigrade, whereby frequency changes 

